Method for efficient hydrogen production from sludge by means of catalytic cracking and reforming promoted by sludge thermal hydrolysis by-product melanoidins

Abstract

A method for efficient hydrogen production from sludge by means of catalytic cracking and reforming promoted by sludge thermal hydrolysis by-product melanoidins, relating to the field of energy recovery from organic solid waste. In view of the problems in high-temperature thermal hydrolysis-pyrolysis processes that melanoidins inhibit sludge decomposition, the composition of pyrolysis gas is complex, and the directional regeneration of H2 is difficult, in the present invention, by-product melanoidins in a high-temperature thermal hydrolysis procedure are extracted to enhance the efficiency of gas production from cracking of thermally hydrolyzed sludge. The sludge is subjected to low-temperature thermal hydrolysis treatment, so that the surface is loose and the degree of organic matter devolatilization is enhanced, thereby promoting gas production from solid-phase cracking of thermally hydrolyzed sludge. Furthermore, melanoidins demonstrate superior reaction catalytic activity due to carboxyl groups and nitrogen-containing structures and achieve the best effect at 2.5 mg / g DW. The total gas production is increased by 6.54%. The melanoidins induce, in mixed gas from the cracking of thermally hydrolyzed sludge, a methane catalytic cracking reaction CH 4®C+2H 2 and a catalytic reforming reaction CH 4+CO 2®2CO+2H 2. The hydrogen yield is increased by at most 35.92%. The present invention effectively solves the engineering bottleneck problems of negative impact of melanoidins and low green energy recovery in the field of thermal hydrolysis-pyrolysis.

Description

A method for efficient hydrogen production from sludge catalytic cracking and reforming using melanin-like byproducts of sludge hydrolysis. Technical Field

[0001] This invention relates to the field of organic solid waste energy recovery technology, specifically to a method for promoting efficient hydrogen production through catalytic cracking and reforming of sludge using melanin-like byproducts of sludge hydrolysis. Background Technology

[0002] Against the backdrop of global resource scarcity and increasingly severe environmental problems, exploring innovative methods for energy recovery and accelerating the construction of a circular economy system are urgent tasks. Wastewater sludge (80% water content, 30-50% organic matter content) is discarded in large quantities as a byproduct from the biological wastewater treatment process of wastewater treatment plants; it is estimated that by 2035, the global annual sludge production will exceed 100 million tons. As a high-value resource (enriched with carbon, nitrogen, phosphorus, etc.), the recycling of wastewater sludge has enormous potential to promote the establishment and operation of a circular economy model.

[0003] Pyrolysis is widely recognized as an emerging technology for the efficient conversion of organic components in sludge into energy-intensive gases (methane and hydrogen). Through a gradient heating mechanism, it can achieve efficient conversion of organic matter within hours. Compared with traditional anaerobic digestion technology, it has significant advantages in terms of low carbon emissions and rapid processing. Simultaneously, hot hydrolysis, as a pretreatment technology, induces cell wall lysis in sludge under high temperature and pressure (50–260 ℃, 0.6–6 MPa), promoting the collapse of the internal structure and loosening of the surface. Sludge solid-phase resource utilization technology based on hot hydrolysis-pyrolysis coupling will further promote the volatilization and release of sludge solid phases and accelerate the volatilization and decomposition reaction, thereby significantly improving the gas production potential of pyrolysis. However, pyrolysis, as a complex thermochemical interaction involving multiple components, produces gases with complex compositions, mainly including C1–C4 gas components such as CH4, H2, CO2, CO, and C2H4. Among various gaseous components, H2 is a zero-carbon, clean, and renewable energy source with a high energy yield (142.35 kJ / g), which is 2.75 times higher than that of other hydrocarbons. Therefore, how to directionally convert pyrolysis gases into H2 is of great significance for solving the problem of large-scale global green hydrogen energy production.

[0004] Although hot hydrolysis, by stimulating the release of intracellular and extracellular organic matter, is considered a promising technology for the efficient conversion of sludge resources, it involves Maillard reactions under high-temperature conditions. Initially, protein amino groups and sugar carbonyl groups undergo heterocyclic reactions to generate colorless intermediates. These intermediates then undergo a series of chain reactions, including cyclization and condensation, to produce recalcitrant byproducts called melanin-like pigments. Melanin-like pigments have been shown to significantly reduce the volatilization of organic matter in sludge and hinder floc degradation and organic matter conversion. Hot hydrolysis treatment technology based on the coupling of alkali addition and photocatalysis effectively mitigates the negative effects of melanin-like pigments. However, the risk of reagent residues poses a significant challenge to the development of green and environmentally friendly new productivity technologies in my country. Summary of the Invention

[0005] This invention addresses the problems of reagent residues, complex pyrolysis gas composition, and difficulties in targeted H2 regeneration in hydrothermal sludge treatment technologies that couple alkali addition and photocatalysis. To achieve efficient conversion of sludge organic matter and green energy recovery, this invention proposes a method that utilizes melanin-like byproducts of hydrothermal sludge treatment to promote efficient catalytic cracking and reforming of sludge.

[0006] The hydrogen method.

[0007] The technical solution adopted by the present invention to solve the above problems is as follows:

[0008] The present invention utilizes melanin-like byproducts of sludge hydrolysis to promote efficient hydrogen production through catalytic cracking and reforming of sludge, comprising the following steps:

[0009] Step 1: Collect sludge. The raw sludge is sieved through a 20-mesh sieve to remove large particles of impurities. It is then allowed to stand at 4 ℃ for 24 h. After obvious stratification appears at the sludge-water interface, the supernatant is slowly poured off to obtain concentrated sludge.

[0010] Step 2: Perform low-temperature hot water hydrolysis on the concentrated sludge, then centrifuge to obtain a solid product. Freeze-dry and grind the solid product to obtain sludge powder. Perform high-temperature hot water hydrolysis on the concentrated sludge, then centrifuge to obtain the supernatant of the hot water hydrolyzed sludge.

[0011] The process of the low-temperature hot water hydrolysis treatment is as follows: the low-temperature hot water hydrolysis temperature is 90 ℃-100 ℃, the pressure is 70×103 Pa-150×103 Pa, and the reaction time is 1 h;

[0012] The high-temperature hydrolysis process is as follows: the high-temperature hydrolysis temperature is 160 ℃-180 ℃, the pressure is 550×103 Pa-885×103 Pa, and the reaction time is 1 h;

[0013] The centrifugation process is to centrifuge at 10,000 rpm for 10 min;

[0014] The solid product was freeze-dried at -55 ℃ for 24 hours.

[0015] Step 3: Extract melanin-like pigments:

[0016] 3.1 Filter the sludge supernatant obtained from the high-temperature hot water hydrolysis treatment in step 2, and then mix the hot water hydrolyzed sludge supernatant with macroporous adsorption resin in a 500 mL flask for adsorption; the macroporous adsorption resin is Amberlite XAD761 ion exchange macroporous adsorption resin.

[0017] The mass ratio of the macroporous adsorption resin to the volume ratio of the supernatant from the hot water hydrolysis sludge is 20 g: 100 mL; the solution is filtered through a 0.45 μm filter.

[0018] 3.2 After the adsorption is completed, the macroporous adsorption resin and the supernatant of the hot water hydrolysis sludge are separated, and then a new macroporous adsorption resin is used to adsorb the supernatant of the hot water hydrolysis sludge twice.

[0019] The adsorption process described in steps 3.1 and 3.2 is as follows: shaking at 150 rpm and 25 °C for 12 hours;

[0020] 3.3 Collect the macroporous adsorption resin after adsorption, and desorb it to obtain a melanin-like solution;

[0021] The desorption process is as follows: First, the macroporous adsorption resin is washed with deionized water; then, hydrochloric acid is used as a solvent to precisely prepare 75% acidified ethanol; the hydrochloric acid content is 36.0-38.0% w / %, the ethanol content is ≥99.7 w / %, and 25 mL of hydrochloric acid and 75 mL of ethanol are measured and mixed evenly.

[0022] Finally, the macroporous adsorption resin was added to 75% acidified ethanol and shaken at 150 rpm and 25 °C for 24 hours.

[0023] 3.4 The obtained melanin-like solution was concentrated and freeze-dried in a freeze dryer for 48 hours to obtain melanin-like powder; the concentration was carried out by rotary evaporation at a concentration temperature of 80 °C.

[0024] Step 4: Co-thermal hydrolysis of sludge and melanin-like pigments to produce hydrogen:

[0025] The sludge powder obtained from the low-temperature hot water hydrolysis treatment in step 2 and the melanoidin obtained in step 3 are mixed evenly and then pyrolyzed in a pyrolysis reactor. The solid residue obtained after pyrolysis is biochar. The tar obtained after pyrolysis is collected in an ice-water bath with CH2Cl2 solution. The gas obtained after pyrolysis is collected through a gas collection bag.

[0026] Furthermore, the pyrolysis chamber was purged with nitrogen at a flow rate of 150 mL / min for 10 min. Then, a certain amount of sludge powder sample was taken and pyrolyzed at 500 °C and 700 °C at a nitrogen flow rate of 20 mL / min and a heating rate of 20 °C / min for 20 min, respectively. Finally, the solid residue was biochar, the tar was collected in an ice-water bath with CH2Cl2 solution, and the gas was collected through a gas collection bag.

[0027] The beneficial effects of this invention are:

[0028] 1. This invention is the first to propose extracting melanin, a byproduct of hot water hydrolysis of sludge, and using melanin for catalytic hot water hydrolysis of sludge to produce hydrogen. Compared with existing technologies that use alkali addition and photocatalysis to eliminate the negative effects of melanin, this invention not only has significant advantages in terms of process cost, but more importantly, it promotes the innovative use of hot water hydrolysis byproducts to promote hydrogen production.

[0029] 2. This invention fully utilizes the superior catalytic performance of the carboxyl and nitrogen-containing structures of melanin-like substances, which can enhance the pyrolysis efficiency of hot water hydrolysis sludge and combine with endogenous metals in the sludge to promote the catalytic performance of derived carbon. The redox capacity of melanin-like substances catalytically cracks and reforms the pyrolysis mixed gas, thereby inducing the conversion of pyrolysis gas into hydrogen. Ultimately, this increases hydrogen production.

[0030] 3. This invention proposes a strategy to enhance the pyrolysis efficiency of hot water hydrolyzed sludge by producing hydrogen through a melanin-induced pyrolysis mixed gas catalytic cracking and reforming pathway: the sludge powder treated with low-temperature hot water has a loose surface and collapsed internal structure, which enhances the degree of organic matter volatilization; furthermore, melanin exhibits excellent catalytic activity due to its carboxyl and nitrogen-containing structure, promoting the release of volatile matter and cracking gas; finally, the melanin-induced pyrolysis mixed gas undergoes CH4 catalytic cracking (CH4C+2H2) and catalytic reforming (CH4+CO22CO+2H2) reactions, resulting in a decrease in CH4 and CO2 yields, thereby increasing the H2 yield. Attached Figure Description

[0031] Figure 1 shows the types and amounts of gas produced by the synergistic pyrolysis of melanoidins and hot water hydrolyzed sludge in Example 1. Example

[0032] Melanoid pigments were mixed uniformly with sludge powder obtained under hot hydrolysis at 90 °C for 60 min at different mass ratios to form experimental groups. The melanoidin concentrations were 2.5 mg / g DW (DW refers to dry sludge) and 5 mg / g DW, named 90-2.5 group and 90-5 group, respectively. Unhydrolyzed sludge (group 0) and hydrolyzed sludge under hot hydrolysis at 90 °C for 60 min (group 90) served as control groups. Pyrolysis was performed using a fixed-bed pyrolysis reactor. The pyrolysis chamber was purged with nitrogen at a flow rate of 100 mL / min for 10 min. Then, 1 g of the experimental sample was pyrolyzed at 700 °C with a nitrogen flow rate of 20 mL / min and a heating rate of 20 °C / min for 20 min. Finally, the solid residue was biochar, the tar was collected in an ice-water bath with CH2Cl2 solution, and the gas was collected through a gas collection bag.

[0033] Figure 1 shows that the total gas production significantly increased in the hot hydrolysis sludge and the 2.5 mg / g DW experimental group, with a maximum increase of 6.54%. Further analysis of the gas composition distribution revealed decreased CH4 and CO2 yields, while H2 yield increased by a maximum of 35.92%. This result is attributed to the catalytic cracking (CH4C + 2H2) and catalytic reforming (CH4 + CO2 → 2CO + 2H2) reactions of CH4. The increased yields of C2H4, C2H6, and C3H8 are related to bond breaking and cyclization of aliphatic compounds, while the decreased CO yield may be attributed to the catalytic reaction between the minerals and melanin-like pigments. Most importantly, this experiment yielded an optimal melanin-like pigment dosage of 2.5 mg / g DW, which has significant practical implications for selecting the optimal dosage in future sludge pyrolysis engineering projects.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for efficiently producing hydrogen from sludge through catalytic cracking and reforming of sludge using melanin-like byproducts of sludge hydrolysis, characterized in that, The method includes the following steps: Step 1: Collect sludge, sieve the sludge and then place it in a refrigerator to concentrate it, thus obtaining concentrated sludge. Step 2: Perform low-temperature hot water hydrolysis on the concentrated sludge, then centrifuge to obtain a solid product. Freeze-dry and grind the solid product to obtain sludge powder. Perform high-temperature hot water hydrolysis on the concentrated sludge, then centrifuge to obtain the supernatant of the hot water hydrolyzed sludge. Step 3: Extraction of melanin-like pigments, specifically including: 3.1 Filter the supernatant obtained from the high-temperature hot water hydrolysis sludge in step 2, and then mix the supernatant with macroporous adsorption resin for adsorption; 3.2 After the adsorption is completed, the macroporous adsorption resin and the supernatant of the hot water hydrolysis sludge are separated, and then a new macroporous adsorption resin is used to adsorb the supernatant of the hot water hydrolysis sludge twice. 3.3 Collect the macroporous adsorption resin after adsorption, and desorb it to obtain a melanin-like solution; 3.4 The obtained melanin-like solution was concentrated and freeze-dried in a freeze dryer for 48 hours to obtain melanin-like powder; Step 4: Co-thermal hydrolysis of sludge and melanin-like pigments to produce hydrogen: The sludge powder obtained in step 2 and the melanin-like powder obtained in step 3 are mixed evenly and then pyrolyzed in a pyrolysis reactor. The solid residue obtained after pyrolysis is biochar. The tar obtained after pyrolysis is collected in an ice-water bath with CH2Cl2 solution. The gas obtained after pyrolysis is collected through a gas collection bag.

2. The method for efficiently producing hydrogen from sludge by-products of sludge hydrolysis (melanin-like substances) using hot water hydrolysis of sludge, as described in claim 1, is characterized in that... In step 1, the concentration process is as follows: the raw sludge is sieved through a 20-mesh screen to remove large particulate impurities, and then left to stand at 4 ℃ for 24 h. After obvious stratification occurs at the sludge-water interface, the supernatant is slowly poured off to obtain concentrated sludge.

3. The method for efficiently producing hydrogen from sludge by-products of sludge hydrolysis (melanin-like pigments) using sludge hot water hydrolysis as described in claim 1, characterized in that... In step 2, the low-temperature hot water hydrolysis process is as follows: the low-temperature hot water hydrolysis temperature is 90 ℃~100 ℃, the pressure is 70×103 Pa-150×103 Pa, and the reaction time is 1 h; the high-temperature hot water hydrolysis process is as follows: the high-temperature hot water hydrolysis temperature is 160 ℃~180 ℃, the pressure is 550×103 Pa~885×103 Pa, and the reaction time is 1 h; the centrifugation process is centrifugation at 10000 rpm for 10 min; the freeze-drying temperature of the solid product is -55 ℃, and the time is 24 hours.

4. The method for efficiently producing hydrogen from sludge by-products of sludge hydrolysis (melanin-like pigments) using sludge hot water hydrolysis as described in claim 1, characterized in that... In step 3.1, the mass ratio of the macroporous adsorption resin to the volume ratio of the supernatant of the hot water hydrolysis sludge is 20 g: 100 mL; the solution is filtered through a 0.45 μm filter.

5. A method for efficiently producing hydrogen from sludge by-products of sludge hydrolysis (melanin-like pigments) using sludge hot water hydrolysis as described in claim 4, characterized in that... The macroporous adsorption resin is Amberlite XAD761 ion exchange macroporous adsorption resin.

6. The method for efficiently producing hydrogen from sludge by-products of sludge hydrolysis (melanin-like pigments) using sludge hot water hydrolysis as described in claim 1, characterized in that... The adsorption process described in steps 3.1 and 3.2 is as follows: shaking at 150 rpm and 25 °C for 12 hours.

7. The method for efficiently producing hydrogen from sludge by-products of sludge hydrolysis (melanin-like pigments) using sludge hot water hydrolysis as described in claim 1, characterized in that... In step 3.3, the desorption process is as follows: First, the macroporous adsorption resin is washed with deionized water; then, hydrochloric acid is used as a solvent to precisely prepare acidified ethanol with a mass fraction of 75%; the hydrochloric acid content is 36.0-38.0% w / s, and the ethanol content is ≥99.7 w / s; 25 mL of hydrochloric acid and 75 mL of ethanol are measured and mixed evenly; finally, the macroporous adsorption resin is added to 75% acidified ethanol and shaken at 150 rpm and 25 ℃ for 24 hours.

8. The method for efficiently producing hydrogen from sludge by-products of sludge hydrolysis (melanin-like pigments) using sludge hot water hydrolysis as described in claim 1, characterized in that... In step 4, the pyrolysis process is as follows: nitrogen flow rate is 150 mL / min, purging time is 10 min, pyrolysis temperature is 500~700 ℃, heating rate is 20 ℃ / min, and pyrolysis time is 20 min.

9. A method for efficiently producing hydrogen from sludge by-products of sludge hydrolysis (melanin-like pigments) using sludge hot water hydrolysis as described in claim 1, characterized in that... In step 4, the optimal dosage of melanin-like powder in hot hydrolyzed sludge powder is 0-2.5 mg / g DW.

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